JP2002363150A - Method and apparatus for separating acetic acid and dimethylformamide by distillation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve low recovery ratio of purified dimethylformamide in distilled separation by forming an azeotropic composition of dimethylformamide with acetic acid. SOLUTION: This invention provides a method and a apparatus for separating acetic and dimethylformamide by distillation comprising eliminating azeotropic relationship between acetic acid and dimethylformamide by using, as an azeotropic agent, toluene which forms azeotropic composition with acetic acid, but does not form azeotropic composition with dimethylformamide and enabling separation of dimethylformamide and acetic acid in high yield by distilling off acetic acid together with toluene from the tower top of distilling tower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for separating and purifying a mixed solution of acetic acid and dimethylformamide, and more particularly to a method for recovering dimethylformamide in a high yield.

[0002]

2. Description of the Related Art Since dimethylformamide and acetic acid form an azeotropic composition, when dimethylformamide containing acetic acid having an azeotropic composition or less is separated by distillation, dimethylformamide is obtained from the top of the column, and dimethylformamide and acetic acid are obtained from the bottom of the column. Is obtained. Since it is difficult to separate the azeotropic composition by distillation, the yield of dimethylformamide obtained is limited, and in the conventional method, acetic acid is removed by a method such as neutralization of acetic acid with an alkali or the like, followed by purification and separation. (JP-A-03-148244, JP-A-07-148244)
No. 173119, Japanese Patent Publication No. 58-57421).

[0003]

Since dimethylformamide and acetic acid form an azeotropic composition, if dimethylformamide containing acetic acid having an azeotropic composition or less is separated by distillation, dimethylformamide is obtained from the top of the column. The highest azeotropic composition of dimethylformamide and acetic acid is extracted from, and dimethylformamide mixed in acetic acid causes separation loss. In particular, if the concentration of acetic acid is close to the azeotropic composition, the majority of dimethylformamide extracted as an azeotropic composition with acetic acid is dimethylformamide, and the ratio that can be separated as dimethylformamide is extremely low. Furthermore, dimethylformamide could not be separated and purified from a mixture containing acetic acid having an azeotropic composition or higher. Further, when acetic acid is removed by a neutralizing agent to improve the yield of dimethylformamide, a large amount of the neutralizing agent is required when the acetic acid concentration is high, and the amount of generated neutralized salts is also large.

[0004]

In the present invention, the present inventors have conceived of using toluene which is azeotropic with acetic acid but not dimethylformamide as an azeotropic agent, and has found an efficient distillation separation method. That is, the distillation separation method of the invention is a distillation separation method of acetic acid and dimethylformamide in which toluene is added to a mixed solution containing acetic acid and dimethylformamide, and acetic acid and dimethylformamide are separated by distillation.

In the present distillation separation method, the mixed solution is
It may contain 1 to 10 times by weight of water with respect to acetic acid.

[0006] Alternatively, water may be added to the mixed solution in an amount of 1 to 10 times the weight of acetic acid.

In this case, the distillation is distillation using a distillation tower, and water can be added to the mixture supplied to the distillation column, or water can be supplied to the distillation column separately from the mixture.
Alternatively, water can be added to the overhead vapor or the condensate distilling from the overhead of the distillation column.

[0008] In the distillation separation method of the present invention, acetic acid, dimethylformamide, water and toluene are supplied to a distillation column. Toluene, acetic acid and water vapor are distilled off from the top of the distillation column. And a distillation step of withdrawing the aqueous phase out of the system and refluxing the oil phase to the distillation column.

Alternatively, a step of supplying acetic acid, dimethylformamide and toluene to the distillation column, distilling the vapors of toluene and acetic acid from the top of the distillation column, and adding water to the vapor at the top or the condensate thereof. And separating the aqueous phase into an oil phase, extracting the aqueous phase out of the system, and refluxing the oil phase to a distillation column.

Further, the distillation separation method of the present invention is a method for separating a mixture containing acetic acid and dimethylformamide by distillation using a two-column distillation column, wherein acetic acid, dimethylformamide, water and toluene are separated by a first distillation column. And distilling the vapors of toluene, acetic acid and water from the top of the first distillation column, separating the liquid obtained by condensing the distilled top vapor into an aqueous phase and an oil phase, and separating the aqueous phase from the system. Extracting the oil phase to the distillation column, refluxing the oil phase to the distillation column, supplying the bottom liquid of the first distillation column to the second distillation column,
A step of extracting dimethylformamide from the top of the distillation column.

Alternatively, there is provided a method in which a mixed solution containing acetic acid and dimethylformamide is separated by distillation in a two-column distillation column, wherein acetic acid, dimethylformamide and toluene are supplied to the first distillation column. The toluene and acetic acid vapors are distilled from the top of the column, and water is added to the distilled vapor at the top or the condensate thereof to separate it into an aqueous phase and a liquid phase. Refluxing to a distillation column, supplying the bottom liquid of the first distillation column to the second distillation column, and extracting dimethylformamide from the top of the second distillation column, and acetic acid and dimethylformamide. It can be a distillation separation method of separating.

Further, the distillation separation method of the present invention is a distillation separation method in which a mixture containing acetic acid and dimethylformamide is distilled using at least three distillation columns, wherein acetic acid, dimethylformamide, water and toluene are subjected to a first distillation. Feeding the column, distilling toluene, acetic acid, and water vapor from the top of the first distillation column, separating a liquid obtained by condensing the distilled top vapor into an aqueous phase and an oil phase, and separating the aqueous phase. Withdrawing the oil phase to the distillation column, feeding the bottom liquid of the first distillation column to the second distillation column, and distilling toluene from the top of the second distillation column, Supplying the bottom liquid of the column to a third distillation column,
Extracting dimethylformamide from the top of the third distillation column, and separating acetic acid and dimethylformamide.

Alternatively, there is provided a method of distilling and separating a mixed solution containing acetic acid and dimethylformamide in a three-column distillation column, wherein acetic acid, dimethylformamide and toluene are supplied to the first distillation column. While distilling toluene and acetic acid vapor from the top of the column, water is added to the distilled top vapor or its condensate to separate into a water phase and an oil phase, and the water phase is extracted out of the system, and the oil phase is separated. Refluxing to the distillation column, supplying the bottom liquid of the first distillation column to the second distillation column, distilling toluene from the top of the second distillation column, and removing the bottom liquid of the second distillation column to the second distillation column. A method of separating acetic acid and dimethylformamide, the method comprising a step of supplying dimethylformamide from the top of the third distillation tower and a step of extracting dimethylformamide from the top of the third distillation tower.

Further, the amount of water previously contained or added may be 1 to 10 times the weight of acetic acid.

The method may further include a step of circulating the bottom liquid of the second distillation column to the first distillation column.

The method may further include a step of circulating the toluene distilled from the top of the second distillation column to the first distillation column.

The method may further include a step of circulating, to the first distillation column, a liquid mainly containing an azeotropic composition of acetic acid and dimethylformamide withdrawn from the intermediate portion of the third distillation column.

Further, high boiling components other than acetic acid and dimethylformamide can be extracted from the bottom of the third distillation column.

The distillation separation apparatus of the present invention comprises at least a first distillation column and a second distillation column.
A top distillate delivery pipe with a condenser is attached, a bottoms delivery pipe is attached to the bottom of each distillation tower, and a acetic acid and dimethylamide mixed solution is supplied to the first distillation tower. And a bottom of the first distillation tower is connected to a supply pipe of the second distillation tower via a first distillation tower bottom delivery pipe.

A distillate whose main component is dimethylformamide is distilled from the overhead fraction delivery pipe of the second distillation tower, and acetic acid and low boiling components are discharged from the overhead fraction delivery pipe of the first distillation tower. Can be distilled off.

The distillation separation apparatus of the present invention comprises at least a first distillation column, a second distillation column, and a third distillation column.
The top of each distillation tower is provided with a top distillate delivery pipe with a condenser, the bottom of each distillation tower is provided with a bottoms delivery pipe, and the first distillation tower is equipped with acetic acid. And a raw material liquid supply pipe for supplying a raw material mixture liquid containing dimethylformamide mixed liquid, distills acetic acid and low-boiling components from the overhead fraction delivery pipe of the first distillation column, and Is connected to a supply pipe of a second distillation tower by a bottoms delivery pipe. In the second distillation tower, toluene is distilled from a top fraction delivery pipe, and a bottom bottom is provided by a bottoms. By delivery piping,
Dimethylformamide is distilled as a main component from the top fraction delivery pipe of the third distillation tower, which is connected to the supply pipe of the third distillation tower.

Further, the top fraction delivery pipe of the second distillation tower is connected to the toluene supply pipe of the first distillation tower, and the toluene can be circulated.

Further, the intermediate pipe of the third distillation column is connected to the first distillation column.
A fraction having the highest azeotropic component of acetic acid and dimethylformamide as a main component can be circulated to the first distillation column by being connected to a raw material supply pipe of the distillation column.

Further, high boiling components can be extracted from the bottoms delivery pipe at the bottom of the third distillation column.

A decanter for separating an aqueous phase and an oil phase is provided at the top of the first distillation column, and a reflux device for refluxing toluene in the oil phase may be provided.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a distillation separation method and apparatus according to the present invention will be described.

In the distillation separation method of the present invention, the raw material liquid to be distilled is a mixed liquid containing acetic acid and dimethylformamide.

A major feature of the distillation separation method of the present invention is that toluene is added to a raw material liquid and distillation is performed. According to the present invention, an azeotropic relationship between acetic acid and dimethylformamide in a distillation column is eliminated by adding toluene to a mixed solution of acetic acid and dimethylformamide and performing distillation, and acetic acid and toluene form a new azeotropic relationship. And a new method for separating acetic acid and dimethylformamide is disclosed. Specifically, the fraction of acetic acid is reduced by distilling acetic acid together with toluene from the top of the distillation column. By distilling this liquid again, an azeotropic composition of dimethylformamide and acetic acid is formed, losing dimethylformamide is reduced, and separation with high yield is enabled.

The distillation separation method of the present invention can be carried out using a usual distillation tower. A rectifying distillation column with reflux is preferred.

Acetic acid and toluene are distilled from the top of the distillation tower.

Acetic acid and toluene distilled off from the top of the first distillation column can be distilled off as they are. Acetic acid can be extracted from the mixture of the distilled acetic acid and toluene using water, and the toluene can be reused. However, this method involves a large loss of toluene. Therefore, it is preferable to separate a mixed solution containing acetic acid and toluene distilled from the top of the first distillation column into an aqueous phase and an oil phase. The distillation separation method of the present invention can efficiently use toluene by adopting the above configuration. In this case, it is preferable that the aqueous phase containing acetic acid and the low-boiling component is discharged, while the toluene of the oil phase is refluxed to the distillation column and recycled. By separating into two liquid phases in this way, the loss of toluene is only a very small amount that is dissolved and discharged in the aqueous phase.

Specifically, the liquid extracted from the top of the tower can be separated into an aqueous phase and a toluene phase by a suitable method such as a decanter. Return the toluene phase, which is the oil phase in the decanter, to the top of the distillation column, or to the raw material supply stage, or to the appropriate toluene supply stage between the raw material supply stage and the top with the toluene phase as the reflux liquid, and discharge the aqueous phase containing acetic acid. By doing so, acetic acid and dimethylformamide can be separated.

As a method for separating into an aqueous phase and an oil phase, water is supplied to a mixture of acetic acid and toluene. Water is
Even if it is added to the raw material liquid, it may be supplied to the distillation column separately from the raw material, or a means for appropriately supplying water to the top or the decanter may be provided. The raw material liquid may contain water in addition to acetic acid and dimethylformamide. It is preferable to adjust the total amount of water including this amount of water. Here, the amount of water to be added may be an amount capable of forming a two-liquid phase, and is particularly preferably 1 to 10 times the weight of acetic acid.

One example of a more specific embodiment of the distillation separation method of the present invention is a method using a two-column distillation column, wherein a mixed solution containing acetic acid and dimethylformamide, toluene, and water are mixed in the first distillation column. , A step of distilling acetic acid and toluene from the top of the first distillation column, a step of taking out dimethylformamide containing acetic acid remaining from the bottom of the first distillation column and supplying it to the second distillation column, a step of second distillation This is a distillation separation method including a step of distilling purified dimethylformamide from a column.

By the step of distilling acetic acid and toluene from the top of the first distillation column, a solution of dimethylformamide having a reduced acetic acid content can be taken out from the bottom of the first distillation column. By supplying this solution to the second distillation column, a high recovery of dimethylformamide can be expected.

From the top of the second distillation column, dimethylformamide purified to the target acetic acid content can be extracted.

From the bottom of the second distillation column, the remaining liquid obtained by removing dimethylformamide from the top of the column to a concentration limited by the residual acetic acid and the composition azeotropic with it is withdrawn.

It is preferable that part or all of the mixed solution of acetic acid and dimethylformamide extracted from the bottom of the second distillation column is returned to the raw material supplied to the first distillation column and circulated. This is because the amount of dimethylformamide recovered can be further improved.

When acetic acid, dimethylformamide, and a substance having a higher boiling point than the azeotropic composition thereof are contained in the mixed solution supplied to the second distillation column, the top of the second distillation column is removed in order to remove them. It is preferable to distill purified dimethylformamide from, and to extract high boiling components from the bottom of the column. Further, it is preferable to extract the dimethylformamide solution containing acetic acid from the middle part of the distillation column. The amount of dimethylformamide recovered can be improved by circulating a part or the entire amount of the dimethylformamide mixture taken out from the intermediate part back to the raw material supplied to the first distillation column.

In the above method using a distillation column, the step of distilling acetic acid and toluene from the top of the first distillation column includes the step of distilling acetic acid, toluene and water from the top of the first distillation column. Separating the mixed liquid containing the aqueous phase and the oil phase, discharging the aqueous phase containing acetic acid and low boiling components,
Refluxing the oil phase toluene to the distillation column.

An example of an apparatus as an embodiment of the distillation separation method of the present invention using the above two distillation towers will be described with reference to a conceptual diagram. FIG. 1 is an example of a distillation separation apparatus 10 of the present invention, and is a conceptual diagram of an apparatus including two distillation towers. The distillation separation device 10 includes a first distillation column 12 and a second distillation column 14. At the top of each distillation tower, condensers 16, 1
The top portion delivery pipes 20 and 22 to which the column 8 is attached are attached. At the bottom of each distillation tower, there is a bottom discharge pipe 2
4, 26 are attached. In this bottom discharge delivery piping,
There is a reboiler.

The first distillation column 12 has a raw material supply pipe 2 to which a raw material mixture containing acetic acid and dimethylformamide is supplied.
8 is attached. In addition, water may be added to the raw material mixture for separating acetic acid and toluene. Water may be added to the raw material mixture in advance, or may be supplied from a water supply pipe (not shown) provided in the first distillation column. The bottom of the first distillation tower 12 is connected to a supply pipe 32 of the second distillation tower 14 by a bottoms delivery pipe 24.

In the distillation separation apparatus 10 shown in FIG. 1, the bottoms delivery pipe 26 provided at the bottom of the second distillation column 14
The raw material is circulated to the first distillation column 12 by the raw material circulation pipe 33. This is because the dimethylformamide in the mixture is more efficiently recovered.

The condensers 16 and 18 at the top of the distillation tower are devices for liquefying the vapor from the top of the distillation tower.
It is arranged between the vapor discharge pipes 34 and 36 and the fraction delivery pipes 20 and 22 from the top of the distillation column. The vapor from the top passes through a condenser, is liquefied, introduced into a decanter 38, and separated into an aqueous phase and a toluene phase. Decanter 3
8 can be provided with a water supply pipe for separation of the water phase oil phase.
The toluene phase, which is the oil phase in the decanter, is refluxed to the distillation column 12 by the toluene reflux pipe 40 as a reflux liquid. Part of the toluene may be refluxed in the feed stage or between the feed stage and the top. The aqueous phase containing acetic acid can be withdrawn from the overhead piping. In this way, acetic acid and dimethylformamide can be separated.

Another embodiment of the distillation separation method of the present invention is a distillation separation method using a three-column distillation column, in which a mixed solution of acetic acid and dimethylformamide and toluene are supplied to a first distillation column. (1) a step of distilling acetic acid and toluene from the top of the distillation column, a step of taking out dimethylformamide containing acetic acid remaining from the bottom of the first distillation column, and supplying it to the second distillation column; Distilling off toluene, supplying dimethylformamide liquid containing acetic acid and high-boiling components at the bottom of the second distillation column to the third distillation column, and distilling purified dimethylformamide from the top of the third distillation column. This is a method that includes a step of letting out.

In this method, a mixed solution of acetic acid and dimethylformamide and toluene are supplied to a first distillation column.
Step of distilling acetic acid and toluene from the top of the distillation column, the first
The process up to the step of taking out dimethylformamide containing acetic acid remaining from the bottom of the distillation column and supplying it to the second distillation column has the same operation as the above-mentioned distillation separation method using two distillation columns.

In the above method using a three-column distillation column, the step of distilling acetic acid and toluene from the top of the first distillation column is performed in the same manner as in the above-described distillation separation method using a two-column distillation column. Separating a mixed solution containing acetic acid, toluene and water distilled from the top of the first distillation column into an aqueous phase and an oil phase, extracting an aqueous phase containing acetic acid and low-boiling components, Refluxing the phase toluene to the distillation column.

Further, the step of distilling residual toluene from the top of the second distillation column in this method comprises the step of removing toluene from a dimethylformamide solution containing partially residual acetic acid extracted from the bottom of the first distillation column. It is especially effective when you do. The solution from the bottom of the first distillation column is supplied to the second distillation column, and all remaining toluene is distilled off from the top of the second distillation column.

The toluene distilled from the second distillation column is supplied to the first distillation column, and the remaining toluene can be recycled.

From the bottom of the second distillation column, a mixed solution of acetic acid and dimethylformamide from which toluene has been removed is supplied to the third distillation column, and purified dimethylformamide is distilled from the top of the third distillation column. The liquid from which dimethylformamide has been removed from the bottom to a concentration which limits the residual acetic acid and its azeotropic composition is the limit.

Part or all of the mixture of acetic acid and dimethylformamide extracted from the bottom of the third distillation column is returned to the raw material to be supplied to the first distillation column, and further separated by distillation to obtain dimethylformamide. Can be improved.

Further, a fraction mainly composed of the highest azeotropic component of acetic acid and dimethylformamide is distilled from the middle part of the third distillation column, and the distilled fraction can be circulated to the first distillation column. This is because the dimethylamide is completely recovered by circulating the solution and separating it again by distillation without discarding the solution.

When the mixture supplied to the third distillation column contains acetic acid, dimethylformamide, and a substance having a higher boiling point than the azeotropic composition thereof, purified dimethylformamide is added to the top of the third distillation column. And extracting a high-boiling component from the bottom of the third distillation column from the bottom of the third distillation column. Using a distillation separation method using a three-column distillation tower is an economical method from the viewpoint of the amount of toluene used and the amount of heat.

FIG. 2 shows an example of the distillation separation apparatus 50 of the present invention for performing the distillation separation method using the three-column distillation tower. The distillation separation device 50 includes at least a first distillation tower 52, a second distillation tower 54, and a third distillation tower 56.
The top of each distillation tower is provided with overhead fraction delivery pipes 64, 66, 68 provided with condensers 58, 60, 62, respectively. The bottom of each distillation tower is a bottoms delivery pipe 70, 7
2, 74 are attached. A reboiler is provided alongside the bottoms delivery pipe.

The first distillation column 52 has a raw material supply pipe 7 to which a raw material mixture containing acetic acid and dimethylformamide is supplied.
6 is attached.

The bottom of the first distillation tower 52 is connected to a supply pipe 80 of the second distillation tower 54 by a bottoms delivery pipe 70.

In the distillation separation apparatus 50 shown in FIG. 2, the bottoms delivery pipe 72 provided at the bottom of the second distillation tower 54
It is connected to a supply pipe 82 attached to the third distillation tower 56. This is because the dimethylformamide in the mixture is more efficiently recovered.

The condensers 58, 60, 6 at the top of the distillation column
Reference numeral 2 denotes a device for liquefying the vapor from the top of the distillation tower, and vapor discharge pipes 84, 86, 88 from the top of the distillation tower.
And the fraction delivery pipes 64, 66, 68. The vapor from the top of the first distillation column is discharged to the condenser 5
After passing through 8, the mixture is liquefied, introduced into a decanter 90, and separated into an aqueous phase and a toluene phase. The decanter 90 may be provided with a water supply pipe for water phase oil phase separation. The toluene phase, which is the oil phase in the decanter, is used as a reflux liquid in a toluene reflux tube 9.
By 2, it is refluxed to the first distillation column 52. Part of the toluene may be refluxed between the raw material supply stage or the raw material supply stage and the top. The aqueous phase containing acetic acid is discharged from the top distillate piping. In this way, acetic acid and dimethylformamide can be separated.

The vapor from the top of the second distillation column 54 is liquefied by the condenser 60, and the remaining toluene is circulated to the first distillation column by the fraction delivery pipe 66.

From the bottom of the second distillation column, bottoms delivery pipe 72
The mixed solution of acetic acid and dimethylformamide from which toluene has been further removed is supplied to the third distillation column from the supply pipe 82 of the third distillation column 56. Vapor is introduced into the condenser 62 from the top of the third distillation column through the vapor discharge pipe 88, and liquefied and purified dimethylformamide is distilled from the distillate distribution pipe 68. From the bottom of the third distillation column 56, a liquid from which dimethylformamide has been removed to a concentration that limits the residual acetic acid and the azeotropic composition thereof is withdrawn from the bottoms delivery pipe 74.

Part or all of the mixture of acetic acid and dimethylformamide extracted from the bottom of the third distillation column 56 is
The raw material is delivered to the first distillation column by a raw material circulation pipe 94. The amount of dimethylformamide recovered can be improved by being returned to the raw material and further separated by distillation.

Further, although not shown, a fraction mainly composed of the highest azeotropic component of acetic acid and dimethylformamide is distilled from the middle part of the third distillation column, and the fraction thus distilled is separated into the first fraction.
It can be recycled to the distillation column. This is because the dimethylamide is completely recovered by circulating the solution and separating it again by distillation without discarding the solution.

Further, when the mixture supplied to the third distillation column contains acetic acid, dimethylformamide, and a substance having a higher boiling point than the azeotropic composition thereof, high boiling components are removed from the bottom of the third distillation column by the third distillation column. It can be extracted from the bottom of the tower.

According to the distillation separation method of the present invention, the components in a mixture of acetic acid and dimethylformamide can be separated well. Depending on the component ratio of acetic acid and dimethylformamide,
For example, it is possible to obtain a recovery rate higher by 10% or more, for example, a recovery rate of 90% or more, as compared with a recovery rate which is a limit when dimethylformamide forms an azeotropic composition.

In the distillation separation method of the present invention, acetic acid and dimethylformamide can be efficiently separated by adding toluene to a mixture containing acetic acid and dimethylformamide. Furthermore, since toluene can be circulated and used, and the mixed solution discharged from each distillation column can be circulated, this is an excellent distillation separation method with almost no waste.

Further, the distillation separation apparatus in which the distillation separation method of the present invention has been carried out achieves the above effects well.

As described above, the embodiments of the distillation separation method and the distillation separation apparatus of the present invention have been described. However, the present invention is not limited to only these embodiments, and does not depart from the gist of the present invention. Within the above, based on the knowledge of those skilled in the art, various improvements, changes, and modifications can be made.

[0068]

EXAMPLES The effects of the present invention will be specifically described with reference to examples, but the present invention is not limited to the following examples, and those skilled in the art depart from the scope of the present invention. Various changes, modifications, and alterations may be made without departing.

Example 1 In a distillation separation apparatus of the present invention as shown in FIG. 1, 80% by weight of dimethylformamide was added to a first distillation column having a decanter for separating an aqueous phase and a toluene phase. A solution containing 8% acetic acid and 12% water was supplied at a flow rate of 100 Kg / Hr. In the decanter, only the light liquid toluene phase is refluxed at the reflux ratio of 30 to the top of the distillation column, and the aqueous phase, which is the heavy liquid of the decanter, is distilled off.
A dimethylformamide solution containing residual acetic acid extracted from the bottom of the first distillation column is supplied to the second distillation column having 20 stages, and the reflux ratio is 1.0, and the extraction amount from the top of the column is 72 kg / h.
By operating at r, purified dimethylformamide containing 0.1% by weight of acetic acid is obtained from the top of the column. About 8 kg / hr of an acetic acid solution containing dimethylformamide is withdrawn from the bottom of the second distillation column. At this time, the recovery rate of dimethylformamide was 90% based on dimethylformamide in the feed solution.

(Example 2) In the distillation separation apparatus of the present invention as shown in FIG.
% Dimethylformamide and 15% acetic acid are supplied at a flow rate of 100 kg / Hr, and water is separately added at 30 kg / hr.
hr. In the decanter, only the light liquid toluene phase is refluxed at the reflux ratio of 25 to the top of the distillation column, and the acetic acid phase, which is the heavy liquid of the decanter, is distilled off. The dimethylformamide solution containing residual acetic acid extracted from the bottom of the first distillation column contains about 1% by weight of toluene,
By feeding to the second distillation column and operating at a reflux ratio of 1.0 and a withdrawal amount of 5 kg / hr from the top, a total amount of toluene is withdrawn from the top of the column, and a dimethylformamide solution containing acetic acid withdrawn from the bottom of the column is removed. And further fed to a third distillation column,
By operating with a reflux ratio of 1.0 and an extraction amount of 65 kg / hr from the top of the column, purified dimethylformamide containing 0.1% by weight of acetic acid can be obtained from the top of the column. From the bottom of the third distillation column, about 3 acetic acid solution containing dimethylformamide
0 kg / hr is extracted. At this time, the recovery rate of dimethylformamide was 76% based on dimethylformamide in the supply liquid.

Example 3 In a distillation separation apparatus as shown in FIG. 1, a first distillation column having a decanter for separating an aqueous phase and a toluene phase was charged with 80% dimethylformamide and 8% acetic acid by weight. And a solution containing 12% water in 10
At a flow rate of 0 Kg / hr, the mixture was supplied with the withdrawn liquid on the bottom side of the second distillation column and supplied. The decanter was used to reflux only the light liquid toluene phase at the reflux ratio of 30 to the top of the distillation column. The aqueous phase, which is a heavy liquid, is distilled off. The dimethylformamide solution containing the residual acetic acid extracted from the bottom of the first distillation column is supplied to the second distillation column, and the column is operated at a reflux ratio of 1.0 and an extraction amount of 75 kg / hr from the top of the column. From the top, purified dimethylformamide containing 0.1% by weight of acetic acid is obtained. About 25 kg / hr of an acetic acid solution containing dimethylformamide is withdrawn from the bottom of the second distillation column, and is mixed with the feed liquid of the first distillation column. At this time, the recovery rate of dimethylformamide was 93% based on dimethylformamide in the supply liquid.

(Comparative Example 1) 85% by weight of dimethylformamide and 15%
% Of acetic acid is supplied at a flow rate of 100 kg / hr, and the distillation column is operated at a withdrawal amount of 50 kg / hr and a reflux ratio of 1 so that 0.1% by weight fraction from the top of the column.
Purified dimethylformamide containing acetic acid is obtained. About 50 kg / hr of an acetic acid solution containing dimethylformamide is withdrawn from the bottom of the distillation column. At this time, the recovery rate of dimethylformamide was about 60% based on dimethylformamide in the feed solution.

Examples 1 to 3 show that the distillation separation method of the present invention in which toluene is added to a mixture of acetic acid and dimethylformamide significantly improves the recovery of dimethylformamide. Furthermore, it was found that the distillation separation device of the present invention effectively separated dimethylformamide.

[0074]

The mixture of dimethylformamide containing acetic acid has conventionally been difficult to separate by distillation at a high recovery rate due to the formation of an azeotropic composition. However, toluene is added by the distillation separation method of the present invention. By doing so, acetic acid could be removed, and the recovery of dimethylformamide was improved.

[Brief description of the drawings]

FIG. 1 is an example of a distillation separation apparatus of the present invention.

FIG. 2 is another example of the distillation separation apparatus according to the present invention.

[Explanation of symbols]

 10, 50; Examples of the distillation separation apparatus of the present invention 12; 1st distillation column 14; 2nd distillation column 16, 18; condensers 20, 22; overhead fraction delivery piping 24, 26; bottoms delivery piping 28; Raw material supply pipe 32; supply pipe of second distillation tower 33; raw material circulation pipe 34, 36; vapor discharge pipe 38; decanter 40; toluene reflux pipe 52; first distillation tower 54; second distillation tower 56; 58, 60, 62; condensers 64, 66, 68; overhead distribution pipes 70, 72, 74; bottoms distribution pipe 76; raw material supply pipe 80; supply pipe of the second distillation column 82; Supply pipe 84, 86, 88; steam discharge pipe 90; decanter 92; toluene reflux pipe 94;

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshihiko Kimura 1-8 Miyamae-cho, Takasago-cho, Takasago-shi, Hyogo Inside Kaneka Kagaku Kogyo Kogyo Co., Ltd. (72) Inventor Shun Wachi Miyamae, Takasago-cho, Takasago, Hyogo Prefecture 1-8 Kanebuchi-Kagaku Kogyo Kogyo Co., Ltd. (72) Inventor Nobuhisa Ota 1-8 Miyamae-cho, Takasago-cho, Takasago City, Hyogo Prefecture Kanebuchi Kagaku Kogyo Kogyo Co., Ltd. (72) Inventor Hiroshi Umino Ibaraki 2205 Narita-cho, Oarai-machi, Higashiibaraki-gun, Japan JGC Corporation Technical Research Institute (72) Inventor Shuichi Oguro 2205 Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki Prefecture Nikko Corporation Technical Research Institute (72) Inventor Nobuo Yoshida Yokohama, Kanagawa 2-3-1 Minatomirai, Nishi-ku, Jichi F-term (reference) in JGC Corporation 4D076 AA16 AA22 AA24 BB08 EA02Z EA20Z FA31 FA34 GA01 JA03 4H006 AA02 AA04 AD12 BB11 BV1 Three

Claims (23)

[Claims] 1. A method for separating acetic acid and dimethylformamide by adding toluene to a mixed solution containing acetic acid and dimethylformamide, and separating acetic acid and dimethylformamide by distillation. 2. The mixed solution is used in an amount of 1 to 1 times by weight of acetic acid.
2. The distillation separation method according to claim 1, wherein the method comprises 0 times by weight of water. 3. The mixed solution is added in an amount of 1 to 1 times by weight of acetic acid.
The distillation separation method according to claim 1, wherein 0 weight times of water is added. 4. The distillation is a distillation using a distillation column,
The distillation separation method according to claim 3, wherein water is added to the mixture supplied to the distillation column, or water is supplied to the distillation column separately from the mixture. 5. The distillation is a distillation using a distillation column,
The distillation separation method according to claim 3, wherein water is added to the overhead vapor or the condensate thereof distilled from the overhead of the distillation tower. 6. A step of supplying acetic acid, dimethylformamide, water, and toluene to a distillation column, distilling vapors of toluene, acetic acid, and water from the top of the distillation column, and condensing the vapor from the top of the distillation column. Separating an aqueous phase and an oil phase,
The distillation separation method according to any one of claims 2 to 4, further comprising a distillation step of extracting an aqueous phase out of the system and refluxing an oil phase to the distillation column. 7. A step of supplying acetic acid, dimethylformamide and toluene to a distillation column, distilling vapors of toluene and acetic acid from the top of the distillation column, and adding water to the vapor at the top of the column or a condensate thereof. 6. The distillation separation method according to claim 1, further comprising the steps of: adding and separating into an aqueous phase and an oil phase, extracting the aqueous phase out of the system, and refluxing the oil phase to a distillation column. 8. A method for separating a mixed solution containing acetic acid and dimethylformamide by distillation using a two-column distillation column, wherein acetic acid, dimethylformamide, water and toluene are supplied to a first distillation column. Toluene, acetic acid, and water vapor are distilled from the tower top, and the liquid obtained by condensing the distilled overhead vapor is separated into an aqueous phase and an oil phase.The aqueous phase is drawn out of the system, and the oil phase is distilled. Refluxing the bottoms of the first distillation column to the second column
Feeding dimethylformamide to the distillation column and extracting dimethylformamide from the top of the second distillation column, and separating acetic acid and dimethylformamide. 9. A method for distilling and separating a mixed solution containing acetic acid and dimethylformamide in a two-column distillation column, wherein acetic acid, dimethylformamide and toluene are supplied to the first distillation column. The toluene and acetic acid vapors are distilled from the top of the column, and water is added to the distilled vapor at the top or the condensate thereof to separate it into an aqueous phase and a liquid phase. Refluxing to the distillation column, supplying the bottom liquid of the first distillation column to the second distillation column, and extracting dimethylformamide from the top of the second distillation column, and separating acetic acid and dimethylformamide. Distillation separation method. 10. A method for separating a mixed solution containing acetic acid and dimethylformamide by distillation using at least three distillation columns, wherein acetic acid, dimethylformamide, water and toluene are supplied to a first distillation column. (1) Distillation of toluene, acetic acid and water vapor from the top of the distillation column. Separate the liquid obtained by condensing the top vapor into an aqueous phase and an oil phase, withdraw the aqueous phase out of the system, and return the oil phase to the distillation column. The bottom liquid of the first distillation column to the second distillation column.
Feeding to the distillation column, distilling toluene from the top of the second distillation column, supplying the bottom liquid of the second distillation column to the third distillation column, and removing dimethylformamide from the top of the third distillation column. A method of separating acetic acid and dimethylformamide. 11. A method for distilling and separating a mixed solution containing acetic acid and dimethylformamide in a three-column distillation column, wherein acetic acid, dimethylformamide and toluene are supplied to the first distillation column. While distilling toluene and acetic acid vapor from the top of the column, water is added to the distilled top vapor or its condensate to separate into a water phase and an oil phase, and the water phase is extracted out of the system, and the oil phase is separated. Refluxing the distillation column, supplying the bottom liquid of the first distillation column to the second distillation column, distilling toluene from the top of the second distillation column, and removing the bottom liquid of the second distillation column to the third column. A distillation separation method for separating acetic acid and dimethylformamide, the method including a step of supplying dimethylformamide to the distillation tower and a step of extracting dimethylformamide from the top of the third distillation tower. 12. The amount of water previously contained or added is:
The distillation separation method according to any one of claims 8 to 11, which is 1 to 10 times by weight of acetic acid. 13. The distillation separation method according to claim 8, further comprising a step of circulating the bottom liquid of the second distillation column to the first distillation column. 14. The distillation separation method according to claim 10, further comprising a step of circulating toluene distilled from the top of the second distillation column to the first distillation column. 15. The method according to claim 10, further comprising the step of circulating, to the first distillation column, a liquid mainly containing an azeotropic composition of acetic acid and dimethylformamide withdrawn from the intermediate portion of the third distillation column. The distillation separation method according to any one of claims 12 and 14. 16. A high-boiling component other than acetic acid and dimethylformamide is extracted from the bottom of the third distillation column.
6. The distillation separation method according to 5. 17. A distillation tower comprising at least a first distillation tower and a second distillation tower, and a top of each distillation tower is provided with a top fraction delivery pipe provided with a condenser, and a bottom of each distillation tower is provided. Is provided with a bottoms delivery pipe, a first distillation column is provided with a raw material supply pipe for supplying a mixture of acetic acid and dimethylamide, and a bottom of the first distillation column is provided with a first distillation column. A distillation separation device connected to a supply pipe of a second distillation tower by a bottom discharge liquid delivery pipe. 18. A fraction whose main component is dimethylformamide is distilled from the overhead fraction delivery pipe of the second distillation tower, and acetic acid and low-boiling components are delivered from the overhead fraction delivery pipe of the first distillation tower. The distillation separation device according to claim 17, wherein is distilled off. 19. At least a first distillation column, a second distillation column, and a third distillation column, and the top of each distillation column is provided with a top fraction delivery pipe provided with a condenser. The bottom of the distillation tower is provided with a bottoms delivery pipe.
The distillation tower is provided with a raw material liquid supply pipe through which a raw material mixture containing acetic acid and dimethylformamide mixed liquid is supplied, and distills acetic acid and low-boiling components from the top fraction delivery pipe of the first distillation tower, Further, the bottom of the first distillation tower is connected to the supply pipe of the second distillation tower by a bottoms delivery pipe, and in the second distillation tower, toluene is distilled from the overhead fraction delivery pipe, A distillation separation apparatus, wherein the bottom is connected to a supply pipe of a third distillation tower by a bottoms delivery pipe, and dimethylformamide is distilled as a main component from a top fraction delivery pipe of the third distillation tower. 20. The distillation separation apparatus according to claim 19, wherein a top fraction delivery pipe of the second distillation tower is connected to a toluene supply pipe of the first distillation tower, and toluene is circulated. 21. An intermediate pipe of the third distillation column is connected to a raw material supply pipe of the first distillation column, and a fraction mainly composed of the highest azeotropic component of acetic acid and dimethylformamide is circulated to the first distillation column. 21. The distillation separation device according to claim 19, wherein the distillation separation device is used. 22. The distillation separation apparatus according to claim 21, wherein a high-boiling component is extracted from a bottoms delivery pipe at the bottom of the third distillation column. 23. A decanter for separating an aqueous phase and an oil phase is provided at the top of the first distillation column, and a reflux device for refluxing toluene in the oil phase is provided. The distillation separation device according to any one of the above.